Engineering 101

Air Bubbling Lizard Inspires “Breathing” Supercapacitor

Our natural world is endlessly inspiring. Recently, a team of scientists used a lizard species to create a “breathing” supercapacitor that performs better than those currently in use.

Supercapacitors are sprinters when it comes to energy storage. They complement rechargeable batteries, compensate for short-term power outages in hospitals and data centers, and buffer for consumption spikes. The current designs, however, don’t have sufficient energy density, so they don’t last long enough.

Modern electric energy storage needs to handle both long-term uses, can act in times of low electricity availability, and be low weight. Unfortunately, methods for increasing energy density have always come at the cost of power density.

A team led by Long Chen, Cheng Lian, Xiangwen Gao, and Chunzhong Li at East China University of Science and Technology (Shanghai, China) and the University of Oxford (UK) is beginning to overcome this challenge.

Anole lizards are common throughout the Americas. These little reptiles create air bubbles around their nose and head, allowing them to breathe underwater when diving for food or escaping predators. 

The team used this rebreathing idea to make their new electrode. They used porous carbon materials, which can hold onto a layer of gas (chlorine) when submerged in a solution of table salt as an electrolyte. They got the most favorable results from multi-wall carbon nanotubes with pores of about 3 nm in diameter.

During charging and discharging, this electrode undergoes a redox reaction in addition to the charge separation usual for supercapacitors. Upon charging, the electrode transfers electrons to the chlorine gas, reducing chlorine to chloride ions, which go into the solution—the electrode “exhales.” Upon discharging, the chloride ions are oxidized back to chlorine, which returns the gas to the electrode’s pores—the electrode “inhales.” No gas escapes the new electrode, and the very rapid reduction/oxidation and mass transfer in the thin layer of gas drastically increases the energy density of the supercapacitor while maintaining an extremely high power density. The capacity remains at the same high level even after thousands of cycles.

The team published their findings in Angewandte Chemie.

 

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